How to set up new annotation fields and who can do that?

Please do this in Account settings > Annotations and Integrations> Annotations. Only Owners, Admins and Accountant roles can set up these fields.

There is one default field - notes. Additional fields can be set up that can be one of the following types: text, number, currency amount, checkbox and dropdown.

Some examples of types of annotation fields you may want to create: chart of accounts with your custom categories, location of spend, team or project.